The present invention relates to stents, and in particular, relates to angioplasty stents adapted to convey therapeutic agents.
The term xe2x80x9cstentxe2x80x9d is intended to indicate devices intended for endoluminal application (e.g. within a blood vessel), normally fitted via catheterization, with subsequent deployment in situ so as to provide a local supporting effect for the lumen. Stents are extensively disclosed in the patent literature, for example co-pending, commonly assigned EP 0 806 190, EP 0 850 604, EP 0 857 470, EP 0 875 215, EP 0 895 759, EP 0 895 760, EP 1 080 738, EP 1 088 528, and EP 1 103 234.
In particular, the present invention falls within the line of research aimed at developing solutions that enable the stent to be used as a vehicle for delivery of active or activatable agents of various nature (e.g., pharmacological agents, radioactive agents, etc.) designed, for example, to inhibit restenosis. Solutions of this sort are described, in the framework of the documents cited above, in EP 0 850 604, EP 1 080 738, and EP 1 103 234.
In particular, EP 0 850 604 describes the possibility of providing, on the surface of a stent, in particular on its outer surface, a sculpturing having the function of increasing the surface area of the stent in such a way as to create undercuts and/or, in general, a surface roughness in order to facilitate application of coatings of active or activatable agents. The sculpturing, consisting for instance of microspheres, may also increase adhesion of the stent to the wall of the vessel being treated.
The most recent clinical developments have revealed that limiting the intervention to coating the surface of the stent with active or activatable agents may encounter various difficulties and/or problems.
First, the amount of agent with which the stent is coated may in actual fact prove insufficient, particularly when the aim is to obtain a release, and hence an action, that is prolonged in time. Further, in applications of vascular angioplasty, the surfaces of the stent, and in particular the inner surface, are subjected to an action of flushing by the blood flow.
Second, for the reason just mentioned, it is desirable that the active or activatable agent should be carried and released prevalently, if not exclusively, on the outer surface of the stent, and not on its inner surface. This is particularly true in the case where the agent applied on the stent is designed to perform an antagonistic function in regard to restenosis. In these situations, the function of the active agent, which is aimed at acting on the outer surface of the stent facing the wall of the vessel undergoing treatment may have unfavorable effects in areas corresponding to the inner surface; for example, the phenomena of neointima formation on the inner surface of the stent, which are considered to be beneficial in the phases subsequent to the implant phase, may be hindered.
In the above general framework, it would be desirable to have available stents that include reservoirs of active or activatable agents, possibly different from one another, available in sufficient quantities to achieve a beneficial effect that may be prolonged over time. Further, it would be desirable to have stents capable of carrying available agents that are different from one another, located selectively in different positions along the stent, with the additional possibility of selectively varying the dosages in a localized way, for instance achieving dosages that are differentiated in the various regions of the stent.
On the other hand, it should not be forgotten that a stent is always configured as a structural element, in the sense that, once placed in the implantation site and brought into its radially expanded condition, the stent must be able to maintain the perviousness of the treated vessel without being subject to appreciable phenomena of contraction or collapse resulting from the radial compressive loads applied on the stent by the walls of the treated vessel.
This explains why the known solutions, aimed at creating on the surface of the stent irregularities such as might contain or enable anchorage of coatings and/or agents of various nature, have so far involved only quite a contained portion of the cross section of the parts (radially expandable annular elements, longitudinal elements of connection) of which the stent is normally composed.
The purpose of the present invention is to make a stent of an improved type which is able to reconcile in an optimal way the characteristics of longitudinal flexibility, which are required, for example, during the phase in which the stent is made to advance towards the implantation site, with the characteristics of plastic behavior required for the stent to be able to perform an altogether effective action of support after being expanded or dilated, minimizing and virtually eliminating any phenomena of recoil.
The object of the present invention is thus to provide a solution that is able to overcome in a decisive way the difficulties and drawbacks referred to above.
It will be appreciated that in the present description and in the annexed claims the term xe2x80x9cstentxe2x80x9d is used in its broadest sense, referring in general terms to any device having an overall tubular shape which is able to support the lumen of a segment of a blood vessel or any other anatomic lumen to prevent blockage of fluid flow. It therefore follows that the scope of the invention must not in any way be understood as being limited to stents for vascular angioplasty. The range of possible application of the invention extends, for example, to stents for treating aneurysms and/or to so-called xe2x80x9cstent-graftsxe2x80x9d.
In one aspect, this invention is a stent for use at an implant site in a vessel comprising a radially expandable tubular body and an active agent for treatment of the implant site, the tubular body having an interior surface and an exterior surface, the tubular body including a plurality of sinusoidal shaped annular elements and a plurality of lambda shaped connection elements, each annular element being connected to at least one other annular element by a plurality of connection elements, each annular element and each connection element having a rectilinear portion and a curved portion, the exterior surface of the tubular body having a plurality of recesses positioned only in the rectilinear portions, the active agent being contained within the recesses, the recesses conferring on the rectilinear portion where they are positioned a hollowed sectional profile of which the recesses occupy from 10% to 60% of the area of the sectional profile, the geometry of the recesses being such that bending moments of inertia of the portions containing the recesses are not substantially reduced. The hollowed sectional profile of the recesses may also range from 20% to 50% of the area of the sectional profile, or may be not less than 30% of the area of the sectional profile. The hollowed sectional profile of the recesses may have undercut areas, a C-shaped profile, a U-shaped profile, a V-shaped profile, or a rectangular profile. The stent also has a longitudinal axis and the longer dimension of the rectangular profile may extends in a direction tangential to or radial to the longitudinal axis. The plurality of recesses may be substantially continuous or discontinuous on the exterior surface of the rectilinear portions of the stent, and each recess may have a substantially well-shaped configuration. The exterior surface of the stent may have a coating of biocompatible carbon material. The plurality of recesses may have a coating of biocompatible carbon material. The active agent may comprise at least two different active agents, and may be present in a non-uniform distribution along the longitudinal axis of the stent.
In a second aspect, this invention is a stent for use at an implant site in a vessel comprising a radially expandable tubular body and an active agent for treatment of the implant site, the tubular body having an interior surface and an exterior surface, the tubular body including a plurality of annular elements and a plurality of connection elements, each annular element being connected to at least one other annular element by at least two connection elements, the tubular body having a plurality of recesses, the active agent being contained within the recesses, the recesses conferring on the elements where they are positioned a hollowed sectional profile of which the recesses occupy a portion of the area of the sectional profile, the geometry of the recesses being such that bending moments of inertia of the elements containing the recesses are not substantially reduced. In a preferred embodiment, the plurality of recesses are on the exterior surface of the stent. The hollowed sectional profile of the recesses may range from 10% to 60% of the area of the sectional profile.
In a third aspect, this invention is a stent for use at an implant site in a vessel comprising a radially expandable tubular body and an active agent for treatment of the implant site, the tubular body having an interior surface and an exterior surface, the tubular body including a plurality of annular elements and a plurality of connection elements, the annular elements and connection elements having portions subject to stress during expansion or use of the stent and portions not subject to stress during expansion or use of the stent, each annular element being connected to at least one other annular element by a plurality of connection elements, the tubular body having a plurality of recesses positioned only in the portions that are not subject to stress during expansion or use of the stent, the active agent being contained within the recesses, the recesses conferring on the portions where they are positioned a hollowed sectional profile of which the recesses occupy a substantial portion of the area of the sectional profile, the geometry of the recesses being such that the characteristic of bending strength of the portions containing the recesses is not substantially reduced. In a preferred embodiment, the hollowed sectional profile of the recesses is not less than 30% of the area of the sectional profile.
In a fourth aspect, this invention is a stent for use at an implant site in a vessel comprising a radially expandable tubular body and an active agent for treatment of the implant site, the tubular body having an interior surface and an exterior surface, the tubular body including a plurality of annular elements and a plurality of connection elements, the annular elements and connection elements having portions subject to deformation during expansion or use of the stent and portions not subject to deformation during expansion or use of the stent, each annular element being connected to at least one other annular element by a plurality of connection elements, the tubular body having a plurality of recesses positioned only in the portions that are not subject to deformation during expansion or use of the stent, the active agent being contained within the recesses, the recesses conferring on the portions where they are positioned a hollowed sectional profile of which the recesses occupy a substantial portion of the area of the sectional profile, the geometry of the recesses being such that the characteristic of bending strength of the portions containing the recesses is not substantially reduced.